"It's super crazy, you think to yourself -- you're sitting in these chairs, and you're like, 'They're having sex with each other,'" he joked. "It's weird. It's like a dynamic shift, because you're just, like, it's wild."

When Stern mused that the timing of Stefani and Shelton's relationship may be wrong due to the two recently going through divorces -- 47-year-old Stefani from Bush frontman Gavin Rossdale and 40-year-old Shelton from country star Miranda Lambert -- Levine disagreed.

"I don't think you can really control those types of matters of the heart," he explained. "I think they found each other at a really interesting time in their lives. I see it as a beautiful thing. Good for them. And I think that love is a good, wonderful thing."